#include<iostream>
#include<cmath>
using namespace std;
int main()
{
	double x, y;
	cin >> x;
	//a+b+c=3*a*b*c^3
	y=cbrt(x);
	y = y * 3;
	printf("%.3lf\n", y);
	system("pause");
	return 0;
}